Liquid air engine

ABSTRACT

1. A liquid air engine comprising a casing, a centerbody located centrally of the casing and extending along the axis thereof, a plurality of precooler heat exchanger cores extending longitudinally and radially from said centerbody at the entrance to said casing in order to precool incoming air, a plurality of deflector plates extending between adjacent sections of said precooler to impart to said incoming air a partially circumferential direction in order to present the full longitudinal face area of the said heat exchanger sections to the incoming air, a plurality of main cooler heat exchanger cores extending longitudinally and radially from said centerbody, means for directing the air discharged from said precooler sections through the full longitudinal face area of said main cooler cores and a single condenser heat exchanger core of circular configuration located aft of said main cooler sections for liquefying the incoming air, said liquid air being utilized as the coolant in said precooler sections and the warmed air discharged from said precooler cores being fed into said centerbody, a source of liquid hydrogen connected to said condenser sections and then to said main cooler sections for use as the coolant, an inner body within said centerbody for receiving the hydrogen discharged from said main cooler cores, a combustion chamber located at the aft end of said centerbody, and means at the end of said centerbody for ejecting the hydrogen from said inner body into a thrust chamber and for ejecting the air into said thrust chamber through said hydrogen for combustion therein.

United States Patent [191 Builder'et al.

[ I Dec. 4, 1973 t LIQUID AIR ENGINE [75] Inventors: Carl H. Builder, Sepulveda; Carl W.

Sessler, Reseda, both of Calif.

[73] Assignee: The Marquardt Corporation, Van

Nuys, Calif.

22 Filed; Aug. 23, 1961 21 App]. No.: 133,445

[52] US. Cl. 60/260, 60/267 Primary Examiner-Samuel Feinberg Attorney-Robert E. Geauque [57] ABSTRACT I. A liquid air engine comprising a casing, a centerbody located centrally of the casing and extending along the axis thereof, a plurality of precooler heat exchanger cores extending longitudinally and radially from said centerbody at the entrance to said casing in order to precool incoming air, a plurality of deflector plates extending between adjacent sections of said precooler to impart to said incoming air a partially circumferential direction in order to present the full longitudinal face area of the said heat exchanger sections to the incoming air, a plurality of main cooler heat exchanger cores extending longitudinally and radially from said centerbody, means for directing the air discharged from said precooler sections through the full longitudinal face area of said main cooler cores and a single condenser heat exchanger core of circular configuration located aft of said main cooler sections for liquefying the incoming air, said liquid air being utilized as the coolant in said precooler sections and the warmed air discharged from said precooler cores being fed into said centerbody, a source of liquid hydrogen connected to said condenser sections and then to said main cooler sections for use as the coolant, an inner body within said centerbody for receiving the hydrogen discharged from said main cooler cores, a combustion chamber located at the aft end of said centerbody, and means at the end of said centerbody for ejecting the hydrogen from said inner body into a thrust chamber and for ejecting the air into said thrust chamber through said hydrogen for combustion therein.

13 Claims, 4 Drawing Figures PATENTEU 41975 sum 1 0r 2 INVENTORS, CARL H. BUiLDER CARL W- SESSLER ATTORNEY PATENTEB DEC 4 1975 SHEET 2 0F 2 INVENTORS CARL H. BUILDER CARL W. SESSLER ATTORNEY LIQUID AIR ENGINE;

This invention relates to a liquid air engine and more particularly to an engine operating on a liquid air cycle and having its components arranged in a manner to result in compact size, lightweight, and improved performance characteristics.

In general, jet engines operating on the liquid air cycle utilize heat exchanger means located within the engine cowling and utilizing alow'temperatureliquid fuel, such as hydrogen, to liquify the incoming air. Thereafter, the liquid air andthe hydrogengas leaving the heat exchanger are fed to a combustion chamber where these substances are combustedto produce jet thrust by expulsion of the combustion products through a jet nozzle. In such engines, a large face area for the heat exchanger means and a large free flow area for the incoming air must beprovided in order to produce sufficient liquid air for the combustion air. Thus, the usual cross flow heat exchanger located across the frontal area of the engine cowling requires a large engine diameter.

In order to increase the performance characteristic of an engine operating on the liquid air cycle, the present invention provides a configuration for the heat exchanger means in which the heat exchanger cores are arranged inradial blanks about acentral header and extend longitudinally of the engine. The use of longitudinally extending heat exchanger cores provides a means of obtaining a large heat exchange face area and also the required free flow area for the incoming air, both of which are required for efiicient engine opera tion. While the frontal area of the engine is not increased in. size, the heat exchanger cores extending rearwardly of the engine result in minimum frontal blockage with the required large heat exchanger area for theair flow. Since the air flow through the inlet to the engine is usually sonic, resulting in a choked inlet, the volume of air flow through the engine inlet is not affected by changesin flight velocity, and is only determined by an air flow restricting area downstream of the engine inlet. The free flow area at the front of the heat exchanger section is one of concern. By turning the heat exchangers into the longitudinal direction, the free flow area required can be acquired without making the engine cross-sectional area much larger than the engine cowl area.

uify the air, can be circularly arranged transversely across the engine diameter. Finally, both the air and the fuel utilized as coolant in the precooler and main cooler stages, respectively, are discharged into the central header or centerbody, with the air and fuel passing rearwardly to the combustion chamber. The centerbody contains an inner body through which the fuel flows, while the air flows through the annular space between the centerbody and the inner body. In the thrust chamber, the air is injected across the hydrogen stream, leaving theend of the inner body, to eliminate the possibility of having combustion travel upstream in the centerbody ducting. Also, injection of the air into the hydrogen provides for good dlispersment of the .air over the hydrogen and since the combustion mixture is hydrogen rich, high combustion efficiency is obtained. The centerbody ducting provides a structural means to stabilize the thrust chamber loadsand air drag loads transmitted to themounting points of the thrust chambet. The use of theliquid airascoolant along the-heat exchanger casing wall, the centerbody wall, and in the first'stage precooler, reduces the hydrogen coolant requirement. Furthermore, the overall weight of theengine isreducedby the reduction in requiredinsulation around the heat exchanger casing. I

It is therefore an object of the present invention to provide an engineheat exchangerarrangement for a liquid air engine, in whichthe heat exchanger cores are arranged to provide largeheat exchange face area with a relative small diameter engine by extending the heat exchangers longitudinally of the engine.

Another object of the invention is to provide amain cooler stage for a-liquid air engine having a plurality of separate sections extending longitudinally of the engine aft of the precooler stage, theliquid coolant for said sections being supplied at a point intermediate the ends thereof in order to provide an increased number of cross-counter flow passes between-the coolant and the incoming air.

A further object of the invention is to provide a centerbody for a liquid air engine which receives both the air discharged from the precooler stage and the: fuel discharged from the main cooler stage. and conducts both of these substances rearwardly along the engine to the combustion chamber.

Another object of the invention is to provide an arrangement of heat exchangers for a liquid air cycle engine in which liquid air is utilized as the coolant in the precooler stage and liquid fuel is utilized as a coolant in the condenser and main cooler stages. y

Another object of the invention is to provide a hea exchanger configuration for a liquid air cycle engine heat exchanger in which the heat exchanger cores are arranged in axially extending blanks about a central header or centerbody, said header being connecteddirectly to the engine thrust. chamber to discharge both the air and the fuel, utilized as coolants in the cores, separately into the thrust chamber.

These and other objects of the: invention not specifically set forth above will become readily apparent from the accompanying description and drawings in which:

FIG. 1 is a diagrammaticillustzrationof the liquid air engine 'ofthe present invention showing the arrangement of the heat exchanger stages and of the centerbody for conductingthe air and fuel to the thrust chamber;

FIG. 2 is a perspective view of the engine structure incorporating thefeatures shown in FIG. 1;

FIG. 3 is a front elevation view along line 33 of FIG. 2; and

FIG. 4 is a transverse section along line 4-4 of FIG. 2.

Referring to the embodiment of the liquid air engine of the present invention shown in FIG. 1, the engine comprises an outer casing 10 containing a centerbody 11 extending axially through the casing; Liquid air is collected at the aft end of the engine in manifold 12 and the manifold is connected to pump 13 by a passage 14. The high pressure discharge from the pump is directed by passage to a manifold 16 which distributes the low temperature air via passage 16a to a plurality of passages 17 running along the exterior of the centerbody 11 and to a plurality of passages 18 running along the inner surface of the casing 10. The forward ends of the passages 17 connect with passages 19 of centerbody dome 71 while space 22 reverses the flow and directs the liquid air through the passages to the outer manifold 21. Also, the air flowing through the passages 18 connects with headers 23 which is also connected with manifold 21 for feeding the tubes 24, of each core 25 of the precooler stage 26. The tubes 24 extend radially toward the centerbody and discharge the warmed air into the space 27 within the centerbody 11. The incoming air passes in cross-counter flow relation with the tubes 24 and has a somewhat circumferential direction as indicated by arrows 28. It is apparent that the plurality of passages 17 serve to cool the exterior of the centerbody 11 and that the plurality of passages 18 serve to cool the interior of the casing 10.

The low temperature liquid hydrogen fuel supply 30 for the engine is contained in a tank 31, and discharge passage 32 connects with a pump 33 which supplies hydrogen to a header 34 through passage 35. Header 34 connects with the coils 36 of the condenser stage 37 and the air entering the condenser stage 37 is fully liquefied and collected in the manifold 12. The manifold collector 12 is formed between the inner surface 38 and the outer casing 10. The hydrogen leaving thhe condenser stage 37 is collected in the header 39 which communicates through a plurality of passages 40 with the core 41 of the main cooler stage 42. Each core has an inlet header 43 located centrally of the cooler tubes. The hydrogen coolant flows from the header 43 both forwardly and rearwardly through the tubes 44 and then reverses direction and flows toward the central discharger header 45. Thus, the cooling fluid makes a plurality of passes in cross-counter flow relationship with the air which is flowing in a somewhat circumferential direction over the tubes 44, as indicated by the arrows 46. Eachvcore 41 of the main cooler stage 42 discharges through a passage 47 into an inner body 48 located within the centerbody 11, so that the gaseous fuel discharged from each core of the main cooler stage is collected within the inner body centrally of the air which has been discharged into the centerbody through tubes 24 of the precooler sections 25.

The passage 50 in the inner body 48 leads to the dis charge openings 51 at the end of the centerbody l1, and the hydrogen fuel is discharged through the openings 51 into the combustion chamber 52. Openings 51 are the gas flow spaces between finger like air injectors 54. Also, the air from precooler stage 26 flows through the annular space 26a surrounding the inner body 48 and is discharged through a plurality of openings 53 in the finger like air injectors 54. Suitable means are contained with the combustion chamber 52 to maintain combustion of the air and the hydrogen so that the high pressure combustion gases can be expanded through the nozzle 55 to produce a jet thrust. Since the combustion in chamber 52 is fuel rich, the large number of air jets from openings 53 provide for good dispersion of the air throughout the hydrogen; The air injection prevents the possibility of combustion upstream in space 264.

A small amount of air is removed from space 26a through the passage 60 and a small amount of fuel is removed from space 50 through passage 61. Both of these passages connect with a combustion chamber 62 of an auxiliary turbine 63. Turbine hub 64 carries blades 65 which are driven by the combustion products leaving the combustion chamber 62, and shaft 66 connects the hub directly to the pump 33. Also, pump 13 is connected to shaft 66 through gears 67 and 68 and shaft 69. Thus, the auxiliary turbine can drive the various accessories for the engine, including the pumps for the air and hydrogen.

The physical structure of the engine of the present invention is illustrated in FIGS. 2 through 4. The casing 10 is built in sections such as 10a, 10b, 10c and 10d with the sections 10a and 10b having a mating flange 70 for mounting the precooler stage 26 to the main cooler. As illustrated, the air passages 18 are located just inside the casing 10 and extend forward to connect with the header 23, which in turn connects with the tubes 24 in each of the precooler cores 25 of the precooler stage 26. The inner air passages 17 extend along the centerbody 11 to passages 19, within dome 71 of the centerbody 11. Space 22 serves as a collector for the air leaving passages 19, to direct said air into passages 20 of each core 25. Passages 19 provide cooling means to dome 71 prior to connecting with passages 20 via space 22. The radial passages 20 connect through manifold 21 with the headers 23 to distribute air, as the coolant, through the tubes 24 of the heat exchanger cores 25. Tubes 24 discharge the air into the centerbody 11 through passages (not shown in FIG. 2). The

passages 17 and 18 are connected with the circular header 16 which is supplied with liquid air by air pump 13 (not shown in FIG. 2).

The hydrogen from the storage tank 31 is pumped to the manifold 34 which in turn connects with the tubes 36 carrying the hydrogen in the condenser stage 37. The hydrogen coolant discharged from the condenser stage 37 is collected in the manifold 39 which connects to the cores 41 of the main cooler stage 42 through the passages 40. The header 43 is located centrally of each of the cores 41, and the tubes 44 extend in both directions away from the header 43, then extend back toward the header and then back away from the header to the secondary header 43a. From the header 43a, the tubes 44 again are directed centrally toward the outlet header 45 which leads directly to the inner body 48 through a passage 47, see FIG. 4.

The gaseous fuel is directed through space 50 to the outlet spaces 51 and the air is directed along the annular passage 26a to the outlet jects 53 in order to discharge the air into the hydrogen within the combustion chamber 52. The high temperature, high pressure combustion products are discharged through the nozzle 55 to produce thrust. The auxiliary turbine 63 is shown located on one side of the nozzle 55 and connected with a gear casing 75 which contains gears such as 67 and 68.

Referring to the construction of the various heat exchanger stages of the engine, eight heat exchanger sections 25 are shown extending radially at the inlet of the casing 10 so that air enters the spaces 76 between each pair of the heat exchanger cores. The air is then turned into the face of each heat exchanger core by a turning or deflection baffle 77 which extends from the forward end of one core to the aft end of the adjacent core. The baffle 77 on the opposite side of each heat exchanger core then directs the cooled air rearwardly in the longipermits a large heat exchange face area to be contained within a. relative small diameter package, and such large heat exchanger area is required in order to obtain the necessary reduction in air temperature in the precooler for the necessary volume of air flow into'the liquid air cycle engine. While the frontal area of the engine determines the volume flow of air (assuming a choked entrance), by turning the heat exchanger frontal area sideways in the longitudinal direction of the engine, the required volume of air can still be obtained through an enlarged heat exchanger surface to provide proper cooling.

The main cooler stage 42 comprises four heat exchanger cores 41 extending radially and longitudinally and each of these cores cools the air leaving two of the precooler cores 25. The air leaving the cores 25 engages end plates 78and curved baffle plates 79 so that all of the air from two of the heat exchanger cores 25 is directed through one of the heat exchanger cores 41. The air leaving each heat exchanger core 41 is directed by another curved baffle plate 79 axially through the circular condenser tubes 36 where the air is finally liquefied and collected in manifold 12. It is understood that the condenser stage 37 receives the coldest hydrogen as the coolant, and that the air entering this section has been substantially reduced in volume by being cooled in the precooler stage 26 and in the main cooler stage 42. Thus, the condenser stage 37. can be circular in form and still provide sufficient heat exchange frontal area to liquefy all the air and discharge only liquid air into the collector manifold 12.

The precooler stage 26 and the front of casing can be constructed of steel to withstand high temperature air entering conditions. The main purpose of the precooler is to increase the maximum speed capability of the engine and to lower the incoming air temperature to a point that aluminum could be used in construction of the maincooler stage 42. The precooler 26 is also used as a temperature control stage, and is used to remove the moisture in the air at low altitudes and low speeds.

The liquid hydrogen enters at the center of each of the four main cooler cores M. to cause the hydrogen flow to be split and to make four passes in crosscounter flow relationship to the incoming air as the hydrogen flows through each of the main cooler cores. In the usual two pass system, the hydrogen would be introduced at one end to the tubes which would make a single pass forward and a single pass rearward to provide a simple two pass system. The full volume of hydrogen would be handled by all of the tubes and therefore, the volume increase restrictions would limit the hydrogen to only the two passes. By the present arrangement, greater heat transfer is achieved over the two pass system, since the four pass system allows the hydrogen to approach more nearly true counter flow with the incoming air, and thus maintain greater heat transfer rates.

The centerbody Ill and the inner body 48 serve as the air and fuel return lines from the heat exchanger stages to the combustion chamber. This arrangement allows a short run of line between the thrust chamber and the heat exchanger cores and since these lines handle warm gases at high pressures, their weight can be kept toa minimum because of the short length involved. At the end of the fuel and-air lines, the air is injected across the hydrogen stream from the air injectors. This arrangement eliminates the possibility of having combustion occur inithe centerbody ducting, and byproviding good fuel and air mixing results in high combustion efficiency in the fuel rich mixture. Further, the centerbody ducting arrangement provides a. structural means to stabilize the thrust chamber loads and air drag loads transmitted to the-mountingflpoints of the engine. Finally, the liquid airflow which is divided and transferred forward along the centerbody wall and along the outer wall of the casing, serves as a heat shield for the centerbody return line and for the heat exchanger casing.

It is therefore-apparent that the, present invention provides a novel structure for the liquid air. jet engine, which is able to handle the necessary air flow with a minimum of frontal area, and which also provides a novel means for handling the gas and air mixtures on their way to the combustion chambers. it is understood that the number of precooler cores 25 and the number of main cooler cores 4] can be varied in any desired manner and that the precooler stage could utilize hydrogen in some of the cores rather than liquid air. Various other modifications are contemplated by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the appended claims.

What is claimed is:

LA liquid air engine comprising a casing, a centerbody located centrally of the casing and extending along the axis thereof, a plurality of precooler heat exchanger cores extending longitudinally .and radially from said centerbody at the entrance to said casing in order to precool incoming air, a plurality of deflector plates extending between adjacent sections of said precooler to impart to said incoming air a partially circumferential direction in order to present the full longitudinal face area of the said heat exchanger sections to the incoming air, a plurality of main cooler heat exchanger cores extending longitudinally and radially from said centerbody, means for directing the air discharged from said precooler sections through the full longitudinal face area of said main cooler cores and a single condenser heat exchanger core of circular configuration located aft of said main cooler sections for liquefying the incoming air, said liquid air being utilized as the coolant in said precooler sections and the warmed air discharged from said precooler cores being fed into said centerbody, a source of liquid hydrogen connected to said condenser sections and then to said main cooler sections for use asthe coolant, an inner body within said centerbody for receiving the hydrogen discharged from said main cooler cores, a combustion chamber located at the aft end of said centerbody, and means at the end of said centerbody for ejecting the hydrogen from said inner body into a thrust chamber and for ejecting the air into said thrust chamber through said hydrogen for combustion therein.

2. in a liquid air jet engine as defined in claim 1, wherein each of said main cooler cores has a central header receiving the hydrogen from said condenser increased heat transfer between the hydrogen and the air.

3. In a liquid air jet engine as defined in claim 1, wherein the collected liquid air is connected to said precooler cores through passages along the outer surface of said centerbody and along the inner surface of said casing in order to provide a heat shield for the centerbody and for the heat exchangers within the casing.

4. A liquid air engine as defined in Claim 1 having a first conduit means for withdrawing air from said centerbody, second conduit means for withdrawing fuel from said inner body, an auxiliary combustion chamber connected with said conduit means for combustion of the withdrawn fuel and air, a turbine driven by the combustion products received from said axuiliary chamber, and pump means driven by said turbine to pump the hydrogen and air through the engine.

5. A liquid air engine comprising a casing having an air inlet, a hollow centerbody extending through said casing, a combustion chamber located at the aft end of said centerbody, an air collection chamber formed at the aft end of said casing between said casing and said centerbody, a plurality of radially and longitudinally extending precooler heat exchanger cores spaced apart around said centerbody at the inlet end of said casing,

a turning baffle extending between the forward end of each core and the aft end of an adjacent core to direct the incoming air entering between said cores through the longitudinal face area of each core to provide a large heat exchange face area, a plurality of main heat exchanger sections located aft of said precooler cores and extending longitudinally and radially between said centerbody and said casing, a second turning baffle for directing the air from said precooler cores through the longitudinal face area of each of said main cooler cores in order to provide a large heat exchange frontal area for furthercooling the precooled air, means for connecting said air collection chamber with said precooler cores to provide a coolant for said precooler cores, means for connecting said main cooler cores with a supply of low temperature fuel to provide a coolant for said main cooler cores, and means for directing the coolant discharged from said precooler cores and from said main cooler cores through separate portions of said centerbody to said combustion chamber.

6. A liquid air engine as defined in claim 5 wherein said low temperature fuel supply comprises liquid hydrogen, said centerbody having an inner body comprising one portion for receiving hydrogen discharged from said main cooler cores, the space exterior of said innerbody in said centerbody comprising the other portion 7 for receiving air discharged from said precooler cores;

the end of said centerbody comprising openings for discharging said hydrogen from said inner body and air from said exterior space into said combustion chamber for combustion therein.

7. A liquid air engine as defined in claim 5, having a single condenser heat exchanger core of circular form located transversely across the end of said engine and between the main cooler cores and said collection chamber for liquefying air received from said main cooler cores.

8. A liquid air engine as defined in claim 6, wherein the hydrogen coolant is introduced to each main cooler core at the center thereof, each of said cores having a pair of four pass tubes through which said hydrogen coolant is equally distributed to provide four crosscounter flow passes with the air passing through the main cooler cores.

9. A liquid air engine comprising a casing having an air inlet, a centerbody extending axially. through said casing, an air collection chamber formed at the aft end of said casing between said casing and said centerbody, a plurality of precooler heat exchanger cores extending longitudinally and radially between said centerbody and said casing at the inlet end of said casing, means connecting said collection chamber to said precooler cores for supplying a coolant to said precooler cores and for discharging said coolant into one portion of said centerbody, a plurality of main cooler cores located aft of said precooler cores and extending longitudinally and radially between said centerbody and said main casing, means for supplying a low temperature fuel to said main cooler cores to provide said main cooler cores and for discharging said coolant to another portion of said centerbody, means for conducting the incoming air successively through the longitudinal face areas of said precooler cores and said main cooler sections, a combustion chamber located at the aft end of said centerbody, said two portions of said centerbody comprising separate passages in said centerbody for separately conducting said coolants to said combustion chamber for combustion therein to produce thrust.

10. A liquid air engine as defined in Claim 9 wherein said centerbody contains an inner body, said one portion of said centerbody comprising the interior of the centerbody around said innerbody and said other portion comprising the interior of said innerbody, said main cooler cores discharging to said inner body and said precooler cores discharging to said centerbody around said inner body in order to separately conduct both of said substances to said combustion chamber.

11. A liquid air engine as defined in Claim 10 wherein the ends of said inner body and said outerbody adjacent said combustion chamber combine to form a plurality of inwardly projecting hollow finger-like injectors defining therebetween a number of slot openings for directing fuel into said combustion chamber, the outer surface of said injectors containing a plurality of surface openings directed in substantially the same di rection as said slot openings in order to mix air with said fuel in said combustion chamber.

12. A liquid air engine as defined in claim 9 having first turning bafi'les located between the forward end of each precooler core and the aft end of adjacent cooler cores for turning the incoming air entering between two adjacent cores into the longitudinal frontal area of said other core, and second turning baffles located aft of said precooler cores for turning the air discharged from said precooler cores through the longitudinal frontal face area of said main cooler cores.

13. A liquid air engine as defined in claim 9 having a circular condenser core located aft of said main cooler cores for condensing air leaving said main cooler core, and a collector formed between said centerbody and said casing for collecting liquid air discharged from said condenser core. i 

1. A liquid air engine comprising a casing, a centerbody located centrally of the casing and extending along the axis thereof, a plurality of precooler heat exchanger cores extending longitudinally and radially from said centerbody at the entrance to said casing in order to precool incoming air, a plurality of deflector plates extending between adjacent sections of said precooler to impart to said incoming air a partially circumferential direction in order to present the full longitudinal face area of the said heat exchanger sections to the incoming air, a plurality of main cooler heat exchanger cores extending longitudinally and radially from said centerbody, means for directing the air discharged from said precooler sections through the full longitudinal face area of said main cooler cores and a single condenser heat exchanger core of circular configuration located aft of said main cooler sections for liquefying the incoming air, said liquid air being utilized as the coolant in said precooler sections and the warmed air discharged from said precooler cores being fed into said centerbody, a source of liquid hydrogen connected to said condenser sections and then to said main cooler sections for use as the coolant, an inner body within said centerbody for receiving the hydrogen discharged from said main cooler cores, a combustion chamber located at the aft end of said centerbody, and means at the end of said centerbody for ejecting the hydrogen from said inner body into a thrust chamber and for ejecting the air into said thrust chamber through said hydrogen for combustion therein.
 2. In a liquid air jet engine as defined in claim 1, wherein each of said main cooler cores has a central header receiving the hydrogen from said condenser core, each of said cores comprising a number of tubes connected with said inlet header and having multiple cross-counter flow pass with the incoming air to obtain increased heat transfer between the hydrogen and the air.
 3. In a liquid air jet engine as defined in claim 1, wherein the collected liquid air is connected to said precooler cores through passages along the outer surface of said centerbody and along the inner surface of said casing in order to provide a heat shield for the centerbody and for the heat exchangers within the casing.
 4. A liquid air engine as defined in Claim 1 having a first conduit means for withdrawing air from said centerbody, second conduit means for withdrawing fuel from said inner body, an auxiliary combustion chamber connected with said conduit means for combustion of the withdrawn fuel and air, a turbine driven by the combustion products received from said axuiliary chamber, and pump means driven by said turbine to pump the hydrogen and air through the engine.
 5. A liquid air engine comprising a casing having an air inlet, a hollow centerbody extending through said casing, a combustion chamber located at the aft end of said centerbody, an air collection chamber formed at the aft end Of said casing between said casing and said centerbody, a plurality of radially and longitudinally extending precooler heat exchanger cores spaced apart around said centerbody at the inlet end of said casing, a turning baffle extending between the forward end of each core and the aft end of an adjacent core to direct the incoming air entering between said cores through the longitudinal face area of each core to provide a large heat exchange face area, a plurality of main heat exchanger sections located aft of said precooler cores and extending longitudinally and radially between said centerbody and said casing, a second turning baffle for directing the air from said precooler cores through the longitudinal face area of each of said main cooler cores in order to provide a large heat exchange frontal area for further cooling the precooled air, means for connecting said air collection chamber with said precooler cores to provide a coolant for said precooler cores, means for connecting said main cooler cores with a supply of low temperature fuel to provide a coolant for said main cooler cores, and means for directing the coolant discharged from said precooler cores and from said main cooler cores through separate portions of said centerbody to said combustion chamber.
 6. A liquid air engine as defined in claim 5 wherein said low temperature fuel supply comprises liquid hydrogen, said centerbody having an inner body comprising one portion for receiving hydrogen discharged from said main cooler cores, the space exterior of said innerbody in said centerbody comprising the other portion for receiving air discharged from said precooler cores; the end of said centerbody comprising openings for discharging said hydrogen from said inner body and air from said exterior space into said combustion chamber for combustion therein.
 7. A liquid air engine as defined in claim 5, having a single condenser heat exchanger core of circular form located transversely across the end of said engine and between the main cooler cores and said collection chamber for liquefying air received from said main cooler cores.
 8. A liquid air engine as defined in claim 6, wherein the hydrogen coolant is introduced to each main cooler core at the center thereof, each of said cores having a pair of four pass tubes through which said hydrogen coolant is equally distributed to provide four cross-counter flow passes with the air passing through the main cooler cores.
 9. A liquid air engine comprising a casing having an air inlet, a centerbody extending axially through said casing, an air collection chamber formed at the aft end of said casing between said casing and said centerbody, a plurality of precooler heat exchanger cores extending longitudinally and radially between said centerbody and said casing at the inlet end of said casing, means connecting said collection chamber to said precooler cores for supplying a coolant to said precooler cores and for discharging said coolant into one portion of said centerbody, a plurality of main cooler cores located aft of said precooler cores and extending longitudinally and radially between said centerbody and said main casing, means for supplying a low temperature fuel to said main cooler cores to provide said main cooler cores and for discharging said coolant to another portion of said centerbody, means for conducting the incoming air successively through the longitudinal face areas of said precooler cores and said main cooler sections, a combustion chamber located at the aft end of said centerbody, said two portions of said centerbody comprising separate passages in said centerbody for separately conducting said coolants to said combustion chamber for combustion therein to produce thrust.
 10. A liquid air engine as defined in Claim 9 wherein said centerbody contains an inner body, said one portion of said centerbody comprising the interior of the centerbody around said innerbody and said other portion comprising the interior of said innerbody, , said main cooler cores discharging to said inner body and said precooler cores discharging to said centerbody around said inner body in order to separately conduct both of said substances to said combustion chamber.
 11. A liquid air engine as defined in Claim 10 wherein the ends of said inner body and said outerbody adjacent said combustion chamber combine to form a plurality of inwardly projecting hollow finger-like injectors defining therebetween a number of slot openings for directing fuel into said combustion chamber, the outer surface of said injectors containing a plurality of surface openings directed in substantially the same direction as said slot openings in order to mix air with said fuel in said combustion chamber.
 12. A liquid air engine as defined in claim 9 having first turning baffles located between the forward end of each precooler core and the aft end of adjacent cooler cores for turning the incoming air entering between two adjacent cores into the longitudinal frontal area of said other core, and second turning baffles located aft of said precooler cores for turning the air discharged from said precooler cores through the longitudinal frontal face area of said main cooler cores.
 13. A liquid air engine as defined in claim 9 having a circular condenser core located aft of said main cooler cores for condensing air leaving said main cooler core, and a collector formed between said centerbody and said casing for collecting liquid air discharged from said condenser core. 